An important concern for radio network operators is to make sure that their networks provide good coverage. It has been seen that a common reason for loss of coverage and other network problems are related to antenna installation problems. For example could a feeder degradation of only a few dBs affect both uplink and downlink coverage. Such degradation can be hard to find and can be left unnoticed forever. For the operator coverage is directly related to the income. The situation becomes even worse as operators tend to reuse sites for different technologies and sometimes reuse the same antenna equipment.
Today, there are no proper tools or methodology for finding these problems. Only the largest problems will be detected through alarms
In a diversity instillation with more than one antenna branch, where one of the received paths is bad or slowly degrading, the uplink diversity will be affected or even lost. Typically base stations or access points for data traffic have two or more receiving antennas and the diversity gain is in the order of 3-5 dB. If an affected antenna path also carries a transmitter then the coverage on the downlink is degraded. For systems with more than one antenna the downlink diversity will be affected or the uplink coverage.
Another problem could be that the antennas are not aligned and thus not covering the same area. Also if the transmitters of the cell are separated, one transmitter on each antenna, then the downlink could be suffering from this misalignment and leading to poor coverage on both uplink and downlink. Similar problems occur in case of mismatch of the antenna diagram on the user side.
Often, third party contractors are responsible for the sites and installation of antennas and the operators have minimal insight in the installation of sites and antenna systems. Common for all these problems are that they are very difficult and some times almost impossible to find.
U.S. Pat. No. 5,970,394 discloses a method of detecting faulty antennas and other components of mobile telephone systems. The method is based on signal strength measurements for detecting inequality in path balance. At least theoretically the signal strength received at the mobile station and the cell site respectively are the same and a statistical analysis is made for the evaluation.
In U.S. Pat. No. 6,266,528 receiving properties of an array of antennas for spatial diversity purposes is described. Long and short term samples of received signal strengths for the respective antenna elements are collected and subjected to a comparing analysis. In US published application 2004/0127261 performance of receive-only diversity antennas with two elements are checked by comparing quality parameters. Ideally there should be no difference and an actual difference could be used for generating an alarm or warming.